Automatic adjustment for elevator brakes



Patented Apr. 6,1948

AUTOMATIC ADJUSTMENT FOR ELEVATOR BRAKES Arthur M. Tarbox, Belmont, Mass, assignor to F. S. Payne 00., Cambridge, Mass, at corporation of Massachusetts Application October 9, 1943, Serial No. 505,631

This invention relates to improvements in a braking system for elevators, and more particularly to the provision 01" means for automatically adjusting the strength of elevator brakes.

My invention is especially applicable to auto matic elevators having spring-pressed friction brakes which are released electromagnetically. In elevators of the automatic type, the brake is automatically applied as the elevator reaches a point a short distance from the floor at which it is to stop. The distance which the elevator travels from the point at which the brake is applied uni t comes to a step may be referred to as the slide. t of course, desired that the elevator should stop level with the floor, but in practice, due to various factors such as the condition of the equipment, variations in load, etc., which cause variations in speed, it is found that the car may not always automatically stop at the desired point, and that this condition can not be completely corrected by the ordinary manual adjustments. Decreasing the slide may make the dilierence in level smaller, but this will require increasing the strength of the brake spring, and the faster stop is not as comfortable to the passengers and increases the wear of the brake linings.

It is an object of my invention to automatically control the force by which the brake is applied in accordance with the speed of the elevator, so that the slide of the elevator car from the instant of applying the brake until the car is brought to a stop will be substantially constant.

It is further an object of my invention to automatically set or adjust the brake for subsequent application while the brak is released, whereby the efifective strength of the brake is increased as the car speed increases and decreased as the car speed falls ofi.

It is a still further object of my invention to provide in combination with a spring-pressed friction brake rotatable means acting upon the brak spring and electrical means for producing a force to turn the rotatable means and compress the brake spring in accordance with the speed of the elevator car.

Further objects and advantages of my improvements will be more readily apparent from the following description of a preferred embodiment thereof as illustrated in the attached drawings, in which Fig. 1 is a plan view of the elevator brake system, the top of the brake being shown in section horizontally thereof;

Fig. 2 is a side elevation of the friction brake Claims. (Cl. 188-171) with a part of the control casing being broken away and shown in section; and

Fig. 3 is a diagrammatic view of the electrical connections.

It will be understood that I have disclosed my improvements in a braking system for elevators, but that the system could be readily designed to apply to an automatic brake for any motor driven load.

The driving motor for the elevator is shown at it. In accordance with standard practice, the motor it drives a winding drum or traction sheave either directly or through gears (not shown). The friction brake l2 shown in Fig. 2 is applied to a brake drum or brake wheel I 4 which may form part of the coupling through which the motor ill drives the elevator. The brak I2 is in general a standard type of spring-applied and electromagnetically released brake, and comprises the brake shoes l6, adjustable shoe stop l8, brake lever 23 pivotally mounted on one of the shoes at El, electromagnet 22, armature 24, and connecting link 26 between the armature 24 and lever 28. The brake shoes are normally urged into engagement with the brake drum by th spring and are held in released position by energize.- tion of the electromagnet 22. A brake of this general type is shown in a patent to Smith No. 1,692,056, issued November 20, 1928.

The brake shoes 15 are formed with clevises 29 at their upper ends which are engaged by the collars 3t and 32. The collars 321 and 32 fit into recesses 31 formed in the clevises 29 which hold the collars against rotation. The rod or shaft 34 is supported at one end by an antifriction bearing 33 carried by collar 30, and at the other end by an antifriction thrust bearing 35 carried by the clevis 6d. The shaft has a high pitch screw thread 35 engaged by the nut 38. The nut 33 is limited in its movement to the right in Fig. 1 by engaging a leather stop 48- on abutment collar 42 fixed to the shaft 34 by a pin 35-. The nut 33 is free to move longitudinally but is restrained from rotation by the guide rods 48 mounted in collar 32 and a ring or collar 45. The rods 38 are provided with adjusting nuts 59 for fixing 3 clevis. 60 connects the lever arm 29 to the shaft 34 through bearing 35 for release of the brake through energization of the electromagnet.

It will be understood that energization of the electromagnet 22 will rock the lever arm 20. The arm 29 initially fulcrums at its upper end and moves theright handbrake shoe 51.6 to which it is connected ,toreleased position intocontact with the stop l8, and finally pushes the clevis to and shaft 34 to the left in Fig. 2, thereby compressing the spring 28. The left hand brake shoe will then be free to gravitally move to released positlon. When the electromagnet is deenergized,the expansion of spring 23 willforcethe brake shoes into frictional engagement with the brakedrum l4.

As thus far described the brake WilLfunction normally. I have provided further means-forvariably increasing the compression of the 31131315528 above its normal compression when the brake is released, and means for controlling such adjustment of the springin accordance with the speed or the elevator. The driving motor it is ,connected through belt 52 to a direct current selfexcited generator The generator in .turn is electrically connected to .a rotating magnet '65, sometimesfknown as atorgue motor. The rotat ingimagnet or torque motor dd is arranged to drive the shaft through the belt Kit and pull ys 19, E2. The shaftfi i .will be turned by th'e torque motor 3% Lin onedirection only so .as .to cause the .nut to travel towards 'thelleft and compress the spring 38. The pitch of screw ,3lis such that the nut willpvercome-statioffriction and-turn the shaft t lbackwards to release the springipressure if the force of the spring overcomes-the torque produced by motor-fit.

The electrical connections are shown in Fig. 3, 'inwhich the A. C. supply lines :are'indicated at 14;, 1'6. The circuit "is connected to the A. C. supplylines includes 'arelay 80 and a SWitCh'BZ. The switchBZ .is controlled by th main elevator controller when'the'movement of the-car is in the upward'direction; there being 'a'similar. switch 82 for control purposeswhenthe .carnrovement is in the'downward direction. Closure of the up switch 'BiZiWill energize the alternating:currentrelay 85). The armature .8 3 of the generatorfi i is connected by the closed :circuit '86 .totherotating magnet 66. The circuit 86 may include 'a variable .resistance 88 to control .the maximum strength of the braking.

:Rotation of'thegeneratorarmature in the residuarmagnetic field willdevelop .a small voltage inthe circuitiafi, and the voltage will rapidly'build up ;as soon 'as the enerator field is connected. Since :the generator "is driven from .the elevator motor, it will reverseits direction Qfrotation accnrdingto the travel of'the'eleilator, and separate circuits are provided for connecting-the generator field-inshunt across the armature in accordance withthe direction of rotation thereof. The up circuit-"99 connects the generator field'ilif across the circuit 85. A variable resistance :94 forms ,a

part'of -circuit TheA/C. relaytil operates three switches'fifi, S3 and The switches 96 and 98 must be closed to "initially complete the circuit 93. It-is todoe understoodthat theswiteh182 will be openedautomatically b-ythe elevator controller-whenpower to theelevatormotor is out on as the car approaches the floor at'which :itis to stop,and means are provided "to keepthe generator freld connected-even thoughthe relay Bills deenergized by epening' of-switch 82. I-have therefore provided a circuit i d2 connected across the circuit 85 in parallel with the generator armature and including the switch 9% and direct current relay H1 5. The circuit its will be closed by actuation of the switch I til, and the energization of the relay iii l will actuate the three switches i 55, m8 and i iii which correspond to the switches \Efi, 9 8 and lid. The switch 1% completes a cirlcuit l t2 across the switch fifi to keep one line of the circuit 9! closed after switch 96 opens. The circuit H2 includes a variable resistance H 5. Similarly, switch H38 completes a circuit lit across the switch 98 and is effective in keeping the other line of circuit Si] closed after the switch Eli-opens. ,liinally, the energization of the .relay .i-ii iismaintained after the switch I til opens iloy :Switeh. 1:56, which completes the circuit [t2 through the connection H3 and part of the circult H5, The switches 36, I68 and H5 Will be heldiinclosed position by the relay ISA until the voltage in the circuit 85 has fallen to a relatively small amount due to slowing up of the elevator.

Separate circuits cease and [52 etc..are provided to control the car when it-is travelling ina downward direction. These circuitscontrol the relays 813 and 1.8.5 and .the switches 55 ,etc. in the same manner as the lip-relays and switches.

While the elevatorjis atrest the brake will be set to hold the car ata position .of rest. The minimum strength of theibrake springifi .is .determined by the relative ,positionof .the bumper id, collar 56, and is adjusted by ,nutsil onthe rods 38. The adjustment of the spring ,for the minimum strength should be suflicient .to hold the car againstrunning away underthe heaviest load that may .be carried, and also sufficient in strength so that the brake will stop the travel of the elevator car eventhoughthere may be failure of the electrical circuits. It will be understood, howeverythat such minimumadjustment .of the springinay-not be sufiicient to stop the car atthe desired floor. The elevator may-be of the type known as single automatic push-button, with a conventional single speed A. C. motorwand controller. On the main elevator controller is an auxiliary, normally open, contact 32 on the up direction switch, and also a normally-open contact 82 on the down direction switch. The car is started by energization-of theelectromagnet 22 to release the-brake and by starting of the motor iii. Simultaneously with application of power to'motor 'i'9,switch 82 or switch '82 will close, depending on whether the "elevator starts up or down. Let :us assume that the car starts up, and switch 82 is closed. Thealternating current will energize rel-ay fifi, closing switches 98 and tilt. At the same time the directcurrent generator-26d starts revolving and building up its voltage due'to the-rotation of its armaturefie in the residual magnetic field. When the-voltage of the generator 'has built up to a sufficient value the direct currentrelay lildwill be energized, thereby closing the switches 'l 96, H38 .and H153. 'This occursiat approxlmatelyzthettime that the elevator car has accelerated and reached its :11ormalrated S e d.

The torque developed by the rotating magnet 55 will be ,governed. .by the speed at which the elevator is travelling, because the voltage detion to compress the spring 28 until the resist- .ances 94 and 941.

ance of the spring balances the turning force. The spring will be compressed an amount which will be determined by the speed of the elevator motor and the characteristics of the generator, the characteristics of the rotating magnet, and the setting of the various control resistances.

When the floor stop opens the up direction contactor on the main control panel, the auxiliary normally open contact 82 will reopen, and control relay 89 will be deenergized to open switches 96, 98 and Ids. The generator armature will still be connected to its field 52 through relay I04, holding the switches H16, H38 and lid The brake will be applied in the usual manner by deenergizing the electromagnet but the strength of the brake will be determined by the amount the spring has been compressed while the car was running. During most of the retardation period, or slide, the relay EM will remain closed and the. generator will continue to furnish current to the rotating magnet. When the voltage of the generator has decreased to a fractional value of its normal voltage, and the speed of the car has dropped to a very low value, the relay I 94 will open and the generator field will no longer be connected to the generator armature. Thereupon the spring 28 will force the travelling nut 38 along screw as, turning shaft 34 backwards until nut 38 contacts the bumper 49. It will be understood that the shaft 34 may start to turn backwards before the relay Hid opens, it the force of the spring is sufficient to overcome the decreasing torque of the rotating magnet This gradual reduction of brake strength during retardation of the car will tend to eliminate the jolt frequently experienced during the final stages of the stopping of single speed elevators. If the controls are properly set, the car will be stopped level with the floor and the car will continue to stop level with the floor under varying conditions of speed and load.

The load speed and energy speed characteristics of an elevator may differ in two directions of travel. The resistance 94 is adjusted to obtain the correct braking for upward motion of the car, and resistance 94 is adjusted to obtain the correct braking for downward motion of the car. The maximum strength of the braking is deter mined by the setting of the resistance 88 in series with the rotating magnet. To control the degree of back-oh of the braking during retardation, resistance H4 is used for the up direction and resistance i for the down direction. Increasing resistances H4 and lid will make the stops more gradual, and decreasing these resistances will make the stops more abrupt.

The relation between the variation in efiective strength of the spring and the variation in speed of the elevator is based upon the particular portion of the generator magnetization curve that is being used determined by the setting of resist- The used portion of the voltage speed curve of the generator may be approximately a straight line, or concave upwards or concave downwards. Thus the increase in the effective strength of the spring may be directly proportional to the variation in speed of the car or may be made to increase at a faster or slower rate as the car speed increases.

My system of adjusting the brake setting spring in accordance with variations in speed of the load has many advantages and could be used in connection with various types of elevators, both manual and automatic, or with other motor driven loads. The minimum amount of braking is used b and the effective life of the brake linings is increased. In moderate speed elevator equipment a part of the braking is done by the frictional resistance of the motor, gearing, guide rails and machine bearings.

The amount of frictiona1 braking required to stop and hold the car at a desired level is determined by the length of the slide. If the length of the slide is increased, the frictional braking does a smaller percentage of the total braking. The brake lining life is increased by taking ad vantage of the inherent braking in the elevator equipment. My improvements are particularly useful with automatic elevators. The equipment required is much less expensive than leveling mechanisms at present in use. I am able to use a single speed A. C. motor instead of a two speed A. C. motor or a variable voltage elevator set. The stops are made gradually without discomfort to the passengers.

Although I have described my improvements in connection with a spring-pressed friction brake of a common type, it will be understood that brakes of other types could be modified to obtain the same results within the spirit of my invention, and that although my improvements are particularly directed to motors and brakes therefor which drive elevators, my improvements could be applied to other motor driven loads where it is desired that the movement of the load and the motor which drives it should be stopped after a predetermined distance of travel of the load or number of rotations of the driving motor by applying the braking in a variabe amount in accordance with the speed of the motor. It will be understood that since it is desired in elevator equipment to keep the slide constant, necessarily the number of rotations of the driving motor from the time that the power is cut ofi and the brake is applied until the motor stops will also remain constant.

I claim:

3.. In an elevator brake, a pair of brake shoes, a pair of collars engaging said brake shoes, a shaft carried by said collars, a bearing on said shaft engaging one or" said collars, a ring slidably mounted on said shaft intermediate said brake shoes, adjustable rods connecting said ring to the other of said collars, a screw thread on said shaft, a nut threaded on said shaft and held against rotation by said rods, a compression spring acting between said nut and said ring, said spring being eiiective to apply said brake shoes, and automatic means responsive to variations in speed of the elevator for turning the shaft while the brake is released to cause said nut to move longitudinally and compress said spring.

2. In combination with a motor, single brake for stopping said motor, means to apply said brake with a normal strength independent of the motor speed, automatic means for producing a variable force responsive to the motor sp ed, reversible means intermediate said brake applying means and said force producing means, said reversible means being movable in one direction by said force producing means to act upon the brake applying means and increase the effective brak ing strength thereof while the brake is released and during the period of brake application, and movable in the opposite direction by the force of said brake applying means overcoming the force of said force producin means, and stop means for limiting the movement of said reversible means by said brake applying means.

3. In combination with a motor, a brake for motor, means to apply gsaid brake with -a normal. trengthindependent-.ofithe motorespced, means ,ior producing a variable sforceresp ns v to -.the motor peed, reversible screw-threaded members intermediate said brakeapplying-means and force producing "means, zone of said screw-thresded members :being movablesin one direotion by said force producingmeansto 'cause theother screw-threaded member to act uponithe brake applying means and increase theeffective braking strength thereofl said last:na-med-screwt readed member being movable in'the opposite ction-by said brake applying means to return d first named screw-threaded member to its normal'position, stop means for limiting'ithe movement of said .screw-sthreaded members'by brakeapplyingmeans.

4. In combination with .a motor, a brake for motor, and means to-apply saidbrake with a normal strength independent of the motor speed, a rotatable shaft, .a nut threaded onsaid shaft, means to hold said nut againstlrotation while permitting lateral movement thereof, means to turn said shaft in a directiomto cause said-nut .to actupon said brakeapplyi-ng means and to increase the effective strength thereof, means tocontrol said shaft turningmeansin ac- COIdELl ce with the speed ofthe motoiysaid shaft being movable in a reverse direction by said nut as the strength of .the brake applying means overcomes the powerappliedto turn said shaft.

5. In combination with a motor, an automatic brake for said motor, means effective to apply said brake with .a normalstrength, a,movable thrust memberacting upon said brake-applying means, stop means for fixing the normal position of saidthrust member, means .for producing a force tending .tomovesaidthrust member. away from said stop meansand increase .the effective strength of said brake applying means and means for controlling saidforceproducingmeans in accordance with the speed of said motor, whereby .the effective braking strength is automatically adjusted while'the brake is .releasedand during the period of brake application by variationsin themotor speed.

'6. In combination with a motor, an automatic brake for said motor, means for applying the brake with a -normal effective strength, means for producinga variable .force acting upon said brake applying means to increase the effective braking strength and means for controlling said foroe'producing means in accordance with variations in speed of said motor whereby the effective braking strength is increased by an increase in motor speed and is decreased by a decrease in the motor speed, said control means providing for an automatic adjustment of the eiTective braking strength while the brake is "released and during the period of brake application.

'7. In an elevator braking system, an elevator motor, a brake therefor, mechanical means for applying the brake, a generator coupled to the motor, a torque motor energized by the voltage developed by said generator and means controlled by the degree of rotation of said torque motor from its normal inactive position and actbrake, a :laterallymovable zscrewathreademmemher, aid spring :rbeing 'TPDSit'iOHEd between said member and the brake, a-rotatable member iin threaded engagement with said laterally :movable member, whereby said rotatable member may cause lateral -movement of the other :memher to increase :the effective braking :force of the spring and the spring reaction may causeireverse rotation of said rotatable member .and :means variably controlled by theispeed ofthe elevator continually tending .to .turn said rotatable memher and adjust "the 'e'fiective strength .of the spring while the. elevator .is in motion :before and during the periodiof brake application.

9. In combination with a motor, ;:a :brake to slow down and stop 'said :mot'or. afterithe :motor power has been cutofi", means ;ior-:app1ying :said brake to said motor, means for releasing asaid brake when power is applied to saidmotonapair of reversible screw-thread members, =variable force producing means tending :to :turn roneiof said members inone directicnionly to produce lateral movement of the other member 3 in a :direction to act upon and variably :increase :the force of the brake applying means while the brakeis-released andduringthe period of -.:brake application, said variableforce producing'means becoming inactive upon stopping of :the;motor and said screw-threaded members :being .automatically returned to normal positions by the reaction of the brake applying means.

10. Iowan elevator braking system'an elevator motor, a brake therefor, spring @means forisettins the brake, a generator coupled to the motor, :a torque :motor electrically connected :to ;the:gen1erator, means for increasing the eiiectivetiforce cf the spring means to apply thebral-ze'withgreater force, means operable by the rotation of the torque :motorfrom its inactive position for con tinuously adjusting the 'means if or increasing cthe efiective force of the spring means while the brake is released and during tRG DBIlOdiDf brake application, whereby the effective -:braking :force is directly responsive to the speedzof the motor and the elevator-will be-stopped in a; substantially uniform distance of travel after the brake is applied.

ARTHUR 1VI. TAR-BQX.

REFERENCES CITED The following references are or file of this :patent:

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